As the first step of the study of the combustion control of solid propellants by electrical discharges, the effects of an arc discharge, which flows along the burning surface, on the burning rate and on the increase of enthalpy of the combustion product were investigated. For specially devised composite propellants, which are composed of Al and Teflon powders, it was shown that the combination can be controlled by an arc discharge; the combustion continues when the arc discharge is applied and is interrupted when the arc discharge breaks. In the present investigation, it was also shown that an arc discharge coupled with a high-frequency electrical discharge has potential as an effective ignition method for solid propellants. For the application of this type of combustion control to an ignitor for a solid propellant rocket motor or to a control rocket motor, this method lacks flexibility in the configuration scale and needs relatively high electric power at the present stage

Kimura, Itsuro

Kobayashi, Tsuruo

Matsuda, Takashi

Tachibana, Takeshi

English

NASA Technical Reports Server

, 
NASA TECHNICAL hIEMORAMDUM 
THE USE OF E L E C T R I C A L  DISCHARGE FOR I G N I T I O N  AND CONTXOL OF 
COMBUSTION OF S O L I D  PROPELLANTS 
T a k e s h i  Tach lbana ,  Tsuruo Kobayashi , - -Takashi  Matsuda and I t s u r o  
Kimura 
T r a n s l a t i o n  o f :  "Hoden n i  yo ru  k o t a i  p u r o p e r a n t o  no t e n k a  oynb i  
nensho s e i g y o , "  Nipponese J o u r n a l  o f  A e r o n a u t i c s  and Space S o c i e t y ,  
V o l .  33,  N O .  3 7 8 ,  1 9 8 5 ,  p p .  4 3 3 - 7  
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION 
WASHINGTON, D . C .  20546 JANUARY 1 9  8 7 
(NASA-TR-88548) T H E  USE CF E I E C I B I C A L  N87-15317 
L l S C H R R G E  EO3 I G N I I I C Y  AND C C E l E C L  GF 
C C N B U S T I C N  Of SCLID FECPELLANlS (Nat ional  
Aeronautics and SFace Rdainistration) 11 p U n c l a s  
1 
CSCL 211 c-3/28 40341 
https://ntrs.nasa.gov/search.jsp?R=19870005884 2020-03-20T12:24:33+00:00Z
The Use of Electrical Discharge for Ignition 
and Control of Combustion of Solid Propellants 
1. Introduction 
It is a well known problem to interrupt and restart combustion of solid 
propellant in order to control the thrust of a solid propellant rocket. Many inves- 
tigations have been made in combustion interruption by rapid pressure reduction 
or combustion restrainer injection in the combustion chamber. There have been 
experiments on ignition and combustion control by injecting a reactive liquid into 
combust ion chamber 1)-3). 
We have been investigating the combustion control of solid propellant by 
electrical discharge. Namely the combustion can be started and maintained by 
an arc discharge current flowing along the surface of solid propellant. The com- 
bustion speed can be controlled by changing the arc current. Enthalpy of the 
combustion product can be increased by the arc electrical energy. Although the 
idea of combustion control by the arc discharge was proposed earlier4), no exper- 
imental investigations have been made. In this report, experimental results of 
the arc discharge effects on solid propellant combustion will be described. The 
arc discharge can be used for the ignition of a solid propellant; its performance 
characteristics will be described as well. 
2. Solid propellant and the experimental setup. 
All the experiments reported here were made at atmospheric pressure. Usual 
1) as well as the following special propellant for solid rocket (Table 1, No. 
propellants were used. 
A propellant was made by compressing a mixture of aluminum powder (80 
mesh) and teflon powder (200 mesh). This propellant has characteristics so that 
ignition and combustion can be controlled by an arc current. The heat generation 
of this propellant is due to the following reaction of florine and aluminum from 
teflon pyrolysis, 
1 
C2F4 -+ 2C + 2F2 - 157kcal/mol, 
A1 + 3/2& + A1F3 + 36lkcal fmol. 
Table 1. Propellants used in the experiment. 
1) Composition, 2) Calorific value, 3) Density, 4) Spontaneous combustion, 
5) Non-spontaneous combustion, 6) without recombination of C and F2, 7) at 
atmospheric pressure. 
Although the present report will limit the description to the experimental 
results of ignition and combustion control, this propellant is known to generate 
relatively high calorie under appropiate combustion condition5). As expected 
from the above reaction equation, in order to increase the generated calorie, 
enough aluminum must be mixed to react with Fa. However, the A1 mixture is 
limited to 30% due to the reduction of propellant strength. In the experiment, 
three types of AZ/(C2F4)n were used as shown in Table 1 No. 1, 2, and 3. The 
calorific values of No. 2, 3, and 4 given in Table 1 were calculated assuming that 
teflon sublimates to C and F2, and F2 reacts with A1 yielding AlF3. The calorific 
value is given by generated heat in the reaction of F2 and A1 subtracting the heat 
required in sublimation. 
Fig, 1(a) and (b) show propellant and electrode arangement for end-burning 
and internal burning cases, respectively. The distance (L) between electrodes was 
fixed at 8 mm. Fig. 2 shows the circuit to supply arc discharge current, consisting 
2 
of a direct current power supply with variable voltage (V,) and a variable resistor 
(Ri) which changes the arc current. Average combustion speed was calculated 
from the propellant weight and the combustion duration. 
END BuRNINi 
SURFACE 
ANODE 
CAHODE 
PROPELLANT - 
PROPELLANT \ 
. . . . . . . . . . .......... .......... .......... 
, PROPELLANT 
m o s r t t w  
I l l G I 1  FREOUENN I 
vs + 
0-370V 
HIGH VOLTAGE 
( a )  ( b )  
Fig. 1 Arrangement of propellant and electrodes for (a) end-burning and (b) 
internal-burning. 
Fig. 2 Circuit for the arc current supply. 
In this experiment propellant ignition by arc discharge was also tried us- 
ing the same electrodes. Namely, an appropriate voltage was applied on the 
electrodes by the arc discharge power supply, and the arc discharge was generated 
by applying high frequency high voltage (3 Mhz, modulated by 100 Hz) on the 
electrodes. This arc discharge was used to ignite the propellant as well as to 
change combustion speed and to increase enthalpy of the combustion gas. 
3. Results of the experiment - 1 (ignition). 
The ignition method presently used for solid propellant has a multi-step mech- 
anism. Namely, an electrical heat ignites an initial explosive which in turn ignites 
a primary explosive which then ignites the propellant. It is more complex to ignite 
solid propellant directly using an arc discharge. Iihara et aL6) has investigated 
an ignition possibility using a single or mntinuous spark discharge, and obtained 
the following results: 1) The discharge ignition of solid propellant requires a rela- 
tively large discharge energy ( at the same time the propellant must be protected 
against an accidental discharge.) 2) For continuous pulse discharge, there is quite 
a long time lag in ignition. 3) It is easier to ignite propellant when an arc dis- 
3 
ORIGINAL PACE R 
OF POOR QUALrrV 
charge is made in a cavity surrounded by propellant rather than on a propellant 
surface6). 
In order to be able to use the same electrode for both ignition and com- 
bustion control experiments, an ignition method using arc discharge induced by 
a high frequency high voltage is adopted. Experimental results on the ignition 
characteristics will be described below. 
Fig. 3 shows the ignition limit for the propellant No. 1 (composite propellant 
commonly used in solid rocket) in the end-burning condition. The figure shows 
the discharge current control resistance (R,) as a function of the arc discharge 
voltage (V8). As seen from the figure, for a lower voltage V,, a smaller R, 
is necessary to ignite the propellant. The propellant never ignited below 200 
V. Decreasing the arc discharge power of the high frequency discharge did not 
change the ignition limit R,, but it caused a time lag of ignition. This time 
lag was not the same even with the same experimental condition and varied 0-3 
seconds. 250 ~,,. . ~ \ , ~ 
$ R i = O n  IGNITION 
SO IGNITION \ 
vs , v 
Fig. 3 Ignition limit by arc discharge. 
Fig. 4 shows the discharge current Id at the ignition limit R, as a fcnctior, 
of the arc discharge voltage. The discharge current at the ignition limit did not 
depend on the discharge voltage. For a range 1-20 A of the discharge current 
after the ignition, the discharge voltage stayed constant at about 200 V. This 
may be related to the fact that the ignition was impossible below 200 V. 
4 
Fig. 4 Ignition limit by arc discharge. 
Although detailed explanation of the ignition mechanism requires future in- 
vestigations, energy required for the ignition will be estimated in the following. 
Energy of the high frequency arc discharge was measured by a calorimeter to be 
about 5.0 W without damping resistor (Ri=O) and 2.4 W with 150n damping 
resistor. The arc discharge time can be measured by interrupting the discharge 
current and inspecting the propellant whether the combustion has started or not. 
With a discharge current 1.5 A, the time was 0.02 seconds, and the required igni- 
tion energy was calculated to be 6 J which is consistent with the value reported 
in ref. 6). It is well known that the combined system of arc discharge and high 
frequency discharge with high breakdown voltage has a good characteristics for 
ignition of flammable gas. The present experiment shows that the similar system 
also works for ignition of solid propellant'). 
The results shown in Fig. 3 and 4 were obtained for propellant commonly 
used in solid rocket. With other propellants A1/(C2F4)n developed for this exper- 
iment, ignition became more difficult and ignition time lag also appeared more 
frequently. As reported in ref 6), it is more difficult to ignite propellant in the 
end-burning condition than in the internal-burning condition. 
4. Experimental results -2 (combustion control). 
Combustion control can be made for Al/(CzF4), composite propellants No. 
2 and 3 by an arc discharge current flowing along the propellant surface. Com- 
bustion control is not possible for the the propellant No. 4 because combustion 
of this propellant can not be suspended. 
Fig. 5 and 6 show the experimental results for the internal-burning condition 
(No. 2 and 3) and the end-burning condition (No. 2), respectively. The ignition 
was not possible at the arc discharge current below 2 A. Above this current, 
combustion could be started or suspended by the discharge current flow. The 
combustion speed r increased with the arc discharge current. As seen in Fig. 5, 
the r - I relation for the propellants No. 2 and 3 are almost identical. This is 
5 
explained by the fact that the pyrolysis in the propellant surface is induced by the 
arc discharge energy and its speed is controlled by the pyrolysis speed of teflon. 
Results for the propellant No. 3 is not shown in Fig. 6 because ignition was 
not possible with the present method. For the propellant No. 4, the combustion 
could not be controlled by the arc discharge current for the internal-burning 
condition. x 1 0 - I  
5- INTERNAL BURNING 
No.2 No.3 
4- A A D = 3 m  
0 0 D=6m 
v) 0 D=10 
\ 
i -t- 
1 4  
I I 1 
0 10 20 30 40 ! 
1, A 
l 
e 
E 
I E  
1 i 
x10-l  
END BURNING . 
L,,, 
0 10 20 30 
1. A 
Fig. 5 Relation between arc current I and propellant line combustion speed 
r (internal-burning, No. 2, No. 3). 
Fig. 6 Relation between arc current I and propellant line combustion speed 
r (end-burning, No. 2). 
6 
ORIGINAL PAGE Is 
O F p o O R Q u m  
Fig. 7 and 8 show the propellant combustion rate riz/W as a function of arc 
discharge power W. The m/W value is large at a small discharge power, but it 
approaches to a constant at large W. 
.- 
I N T E R N A L  B U R N I N G  
L-8. 
7 \ 1 6 r  l4 No.2 N0.3 
12 A A D = 3 m  
L 
0 
I 
1 2 3 4 5 
W ,  kw 
# 4 5 
0 1 2 3 
W, kw 
Fig. 7 Relation of arc discharge power W and propellant mass combustion 
rate rh/W (internal-burning, No. 2, No. 3). 
Fig. 8 Relation of arc discharge power W and prope!!ant mass combustion 
rate rit/W (end-burning, No. 2). 
The ratio of generated chemical energy and arc discharge power can be ex- 
pressed by Q h / W  in terms of calorific value Q per unit propellant weight. In 
order to control combustion using arc discharge, this ratio needs to be large. But 
to increase enthalpy of the combustion product, a smaller ratio is more desirable. 
For internal-burning of the propellant No. 3, Qm/W is 0.1 - 0.5 (Q=5950 J/g, 
h/ W=1.7-8.0x 10-5g/J). Since flammable gas combustion is extremely acceler- 
ated by a smallarc discharge energ;), it is expected to be able to obtain a large 
Qm/W ratio by finding an appropriate propellant and discharge condition. 
Fig. 9 shows effects of the arc discharge on combustion of cornm-only used 
composite propellant No. 1 (Pb/Al/AP, self-flammable). The propellant grain 
has an inner radius 3 mm and an outer radius 7 mm. The average line com- 
bustion speed is shown as a function of the arc discharge current. There is a 
threshold in the arc discharge current for both end-burning and internal-burning 
7 
conditions. Below this threshold current, the arc discharge current is : r e p e l l e d  
from the combustion surface by the combustion gas flow, and the arc discharge 
energy is spent to heat the combustion gas. 
END BUPNING 
i 
Fig. 9 Relation between arc discharge current I and propellant line combus- 
tion speed r (No. 1). 
5.  Summary. 
It was shown in this experiment that a combined system of high frequency 
electrical discharge and direct current arc discharge has good characteristics 
for ignition of solid propellant. For commonly used propellant, once the com- 
bustion is started, it can not be interrupted even if the arc discharge is stopped. 
However, for the specially made propellant (No. 2 and 3) for this experiment, 
combustion can be controled by the arc discharge. There are two typical effects 
of arc discharge on propellant combustion; namely, effect on propellant p y r o l i s  i s  
and heating of combustion product. 
High temperature gas jet produced by sublimation of solid propellant by arc 
discharge and chemical reaction of the gas produced by the sublimation can be 
used as a high temperature heat generator in place of usual plasma jet. Appli- 
cations of this system for solid rocket ignition or secondary propulsion rocket 
motor (electrical heating type) are limited due to the limitation of arc discharge 
frequency and relatively large power requirement. 
8 
REFERENCES. 
1) Hiroki, T. and Fletcher, E. A.: Theoretical Study of Propellant Behavior 
during Thrust Chamber Depressurization, AIAA J. 7 (1969), pp. 1884-1890. 
2) Hansawa, M.: Combustion Interruption Theory by Rapid Pressure Reduc- 
tion, Joural of Aeronautics and Space Society of Japan, 25 (1977), pp. 349-355. 
3) Itsushiro, T.: Thrust Interruption and Control of Solid Propellant Rocket, 
Journal of Aeronautics and Space Society of Japan, 18 (1970), pp. 297-307. 
4) Lawton, J. and Weinberg, F. J.: Electrical Aspects of Combustion, Claren- 
don Press, Oxford, 1969. 
5) Tachibana, T.: Investigation of Plasma Jet Utilizing Solid Sublimation, 
Thesis, Faculty of Engineering, University of Tokyo. 
6) Iihara, S.: Investigation of Ignition Characteristics of Solid Propillant by 
Spark Discharge, Thesis, Faculty of Engineering, University of Tokyo, 1981.3. 
7) Kumagai, S., Sakai, T. and Kimura, I.: Mechanism of Ignition of Gasses 
by Composite Sparks, Journal of the Faculty of Engineering, University of Tokyo, 
XXIV (1953), pp. 9-23. 
8) Kimura, I. and Imajo, M.: An Experimental Investigation of an Arc-Heated 
Stirred Reactor, 16th Symp. (int.) on Combustion, pp. 809-815, 1976. 
9 
I 
and I .  Ximura 
I 
5. b 1 W r n t . r )  N.~t.O 
T r a n s l a t i o n  o f :  "Hoden n i  yoru  k o t a i  p u r o p e r a n t o  no t e n k a  
oyob i  nensho  s e i g y o , "  Nipponese J o u r n a l  o f  A e r o n a u t i c s  and 
Space S o c i e t y ,  Vol .  33, No. 378, 1 9 8 5 ,  p p .  433-7 
& A b o t r c d '  
A s  t h e  f i r s t  s t e p  o f  t h e  s t u d y  o f  combust ion  c o n t r o l  o f  s o l i d  
p r o p e l l a n t s  by e l e c t r i c a l  d i s c h a r g e s ,  t h e  e f f e c t s  o f  a n  a r c  
d i s c h a r g e ,  which f lows  a long  t h e  Surn ing  s u r f a c e ,  o n  t h e  bu rn  
i n g  r a t e  and on t h e  i n c r e a s e  o f  e n t h a l p y  o f  t h e  .combustion 
p r o d u c t  were i n v e s t i g a t e d .  
p r o p e l l a n t s ,  which a r e  composed o f  A 1  powder and t e f ' l o n  pow- 
d e r ,  i t  was shown t h a t  t h e  combust ion can  be c o n t r o l l e d  by an 
a r c  d i s c h a r g e ;  t h e  combust ion c o n t i n u e s  when t h e  a r c  d i s -  . 
c h a r g e  i s  a p p l i e d  and i s  i n t e r r u p t e d  when t h e  a r c  d i s c h a r g e  
b r e a k s .  I n  t h e  p r e s e n t  i n v e s t i g a t i o n ,  i t  was a l s o  shown t h a l  
a n  a r c  d i s c h a r g e  coup led  w i t h  a h i g h  f r e q u e n c y  e l e c t r i c a l  
d i s c h a r g e  h a s  p o t e n t i a l i t y  as  a n  e f f e c t i v e  i g n i t i o n  method 
f o r  s o l i d  p r o p e l l a n t s .  
i o n  c o n t r o l  t o  an  i g n i t o r  f o r  a s o l i d  p r o p e l l a n t  r o c k e t  
m o t o r  o r  t o  a c o n t r o l  r o c k e t  m o t o r ,  t h i s  method l a c k s  
f l e x i b i l i t y  i n  t h e  c o n f i g u r a t i o n  s c a l e  and n e e d s - a  r e l a t i v e l :  
s o l i d  p r o p ? l y a w e  
For s p e c i a l l y  d e v i s e d  compos i t e  
For  t h e  u s e  o f  t h i s  t y p e  o f  combust-  
p i p ~ t r l r  nower a t  p r e s e n t  s t a g e .  
L - 
18. M a w h n n  S W ~  '70 b 4. (mute4 
combust i o n  con  t r o 1 
i g n i t i o n  U n c l a s s i f i e d  a n d  U n l i m i t e d  I 
I 
. .  


The use of electrical discharge for ignition and control of combustion of solid propellants

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